Ink jet recording head

Abstract: An ink jet recording head formed by laminating and fixing: a flow path forming plate (3) having through holes (3a) for defining pressure producing chambers (9), ink supply inlets (10), and a common ink chamber, a nozzle plate (2) having nozzle openings (1) communicating with the pressure producing chambers (9), and a vibration plate (4) having diaphragm portions (4e) that are resiliently deformed in response to displacement of piezoelectric vibration elements (6) one upon another with an adhesive so as to be watertight. The vibration plate (4) has frame-like thick wall portions (4b,4c,4d) that extend as far as to the ink supply inlet (10) side of the pressure producing chamber (9) as well as to the inner side of the nozzle opening (1), and portions closer to a piezoelectric vibration element (6) than to both ends of the pressure producing chamber (9) are made to be supported by a base (7). As a result of this construction, a nonsupported region of the pressure producing chamber (9) can be shortened, which in turn improves the rigidity of a substrate unit (5) as a whole.

Description: The invention relates to an ink jet recording head and a substrate unit for an ink jet recording head that jets droplets of ink by displacing a vibration plate using piezoelectric vibration elements. An ink jet recording head using a piezoelectric vibration element of vertical vibration mode as a drive source, requiring only a small area of abutment of the piezoelectric vibration element against the vibration plate, can achieve an arrangement density of a pressure producing chamber as high as 90 dpi or more. As shown in Fig. 14, such a recording head is fabricated into a single body by integrally fixing a substrate unit K to a base L. The substrate unit K is formed by laminating and fixing a flow path forming plate D, a nozzle plate F, and a vibration plate J with an adhesive so as to be watertight. The base L has a piezoelectric vibration element G, an ink supply pipe, and the like attached thereto. The flow path forming plate D has through holes defining a pressure producing chamber A, an ink supply inlet B, and a common ink chamber C; the nozzle plate F has a nozzle opening E communicating with the pressure producing chamber A; and the vibration plate J has a diaphragm portion H that is resiliently deformed in response to displacement of the piezoelectric vibration element G. In the thus constructed ink jet recording head, the substrate unit must be fixed to the base so as to cause the diaphragm portion H to confront the base so that the diaphragm portion H can be abutted against the tip of the piezoelectric vibration element G. For this reason, the substrate unit is fixed to the base L so as to keep away from the pressure producing chamber A so that the base L does not come in contact with the diaphragm portion H. To improve the pressure producing chamber arrangement density in an attempt to increase resolution, the length of the pressure producing chamber A must be increased in the axial direction since a predetermined capacity of the pressure producing chamber A must be ensured. However, the region confronting the pressure producing chamber A is a nonsupported region S1 that is not supported by the base L, and this region is long. As a result, when such region is given a predetermined displacement "a" by the piezoelectric vibration element G to jet a droplet of ink, the nonsupported region S1 of the substrate unit K becomes susceptible to flexion as shown by the broken lines in Fig. 14, thereby imposing the problem of impairing printing quality. In addition, positional accuracy of the abutment of the tip of the piezoelectric vibration element G is an extremely important factor for such a high resolution. Therefore, to achieve the required accuracy, an island portion M, which is a thick wall portion formed in almost middle of a region causing deformation of the pressure producing chamber, is formed, and the tip of the piezoelectric vibration element G is abutted against such island portion M, as disclosed in Japanese Unexamined Patent Publication No. 3-15555. This construction allows the displacement of the piezoelectric vibration element G to be transmitted through the island portion M even if the position of abutment of the piezoelectric vibration element G is slightly shifted. Therefore, a predetermined displacement can be given to the diaphragm potion H. However, for such an extremely high resolution as 180 dpi or more, inaccuracies in relative position between the island portion M and the pressure producing chamber A are easy to occur, causing the pressure producing chamber A to be deformed inconsistently and thereby imposing the problem of impairing printing quality. Further, to reduce the pitch of the pressure producing chamber A, the partition wall defining the pressure producing chamber A becomes thin, which in turn reduces rigidity. As a result, one pressure producing chamber is deformed by contraction and expansion of a piezoelectric vibration element that drives another pressure producing chamber adjacent to such one pressure producing chamber, causing a so-called satellite. Moreover, the degree of deformation of the pressure producing chamber by the expansion of the piezoelectric vibration element is reduced, thereby imposing the problem of dropping ink jetting efficiency. EP-A-0 563 603 describes a thick wall portion at a region confronting the partition wall defining the pressure producing chamber. The width of this thick wall portion corresponds to the width of the partition wall. The invention has been made in consideration of the aforementioned problems and an object of the invention is, therefore, to provide an improved substrate unit for an ink jet recording head and an improved ink jet recording head. This object is solved by the substrate unit for an ink jet recording head according to independent claim 1 and the ink jet recording head according to independent claim 14. Further advantageous features, aspects and details of the invention are evident from the dependent claims, the description and the drawings. The claims are intended to be understood as a first non-limiting approach of defining the invention in general terms. According to a specific aspect of the present invention, a substrate unit is provided in which the non-supported region of the pressure producing chamber is made as short as possible so as to increase the rigidity of the substrate unit. Another aspect of the invention is to provide a novel ink jet recording head capable of reducing the effect of fabrication inaccuracies upon printing quality to a smallest possible degree. To achieve the above aspects, the invention is preferably applied to an ink jet recording head formed by fixing a substrate unit to a base, the substrate unit being formed by laminating and fixing a flow path forming plate, a nozzle plate, and a vibration plate with an adhesive so as to be watertight, the flow path forming plate having through holes defining pressure producing chambers, ink supply inlets, and a common ink chamber, the nozzle plate having nozzle openings communicating with the pressure producing chambers, the vibration plate having diaphragm portions, each diaphragm portion being resiliently deformed in response to displacement of a piezoelectric vibration element. In such ink jet recording head, the vibration plate has a frame-like thick wall portion formed close to a side of the ink supply inlet of the pressure producing chamber and to a side of the nozzle opening, the thick wall portion being thicker than the diaphragm portion and extended so as to be island-like toward the piezoelectric vibration element, and a region confronting the frame-like thick wall portion is made to serve as a region for bonding the substrate unit to the base. The frame-like thick wall portion extending toward the piezoelectric vibration element is preferably supported by the base. As a result of this construction, the nonsupported region of the pressure producing chamber can be made as short as possible, which in turn allows the base to receive force applied by the piezoelectric vibration element and thereby increases the rigidity of the substrate unit. Fig. 1 is a perspective view showing an embodiment of an ink jet recording head of the invention in unfabricated form; Fig. 2 is a sectional view showing an embodiment of a piezoelectric vibration element used for the head of Fig. 1; Fig. 3 is a partially sectional perspective view showing a region at which a substrate unit and piezoelectric vibration elements of the head of Fig. 1 are abutted against one another in enlarged form; Fig. 4 is a diagram showing the position of a flow path forming plate relative to a vibration plate of the head of Fig. 1; Fig. 5 is a sectional view taken along a line A-A of Fig. 4; Fig. 6 is a sectional view taken along a line B-B of Fig. 4; Fig. 7 is a sectional view showing misalignment between the vibration plate and the flow path forming plate as well as overflow of an adhesive that bonds the vibration plate to the flow path forming plate when the head of Fig. 1 is being fabricated; Fig. 8 is a diagram showing a structure of a section taken along an axial line of a pressure producing chamber; Fig. 9 is a diagram showing a second embodiment of the invention in the form of an upper surface structure of the vibration plate; Fig. 10 is a diagram showing a third embodiment of the invention in the form of an upper surface structure of the vibration plate; Fig. 11 is a diagram showing a fourth embodiment of the invention in the form of an upper surface structure of the vibration plate; Fig. 12 is a diagram showing an embodiment in which piezoelectric vibration elements of flexion vibration mode are used. Fig. 13 (A) is a sectional view showing an exemplary conventional ink jet recording head; Fig. 13 (B) is a diagram schematically showing overflow of an adhesive; and Fig. 14 is a diagram showing an exemplary conventional ink jet recording head. Details of the invention will now be described with reference to the embodiments shown in the drawings. Fig. 1 shows the general aspect of a recording head of the invention. In Fig. 1 reference numeral 2 denotes a nozzle plate having nozzle openings 1 formed therein; 3, a flow path forming plate having through holes 3a defining pressure producing chambers 9, through holes or grooves 3b defining ink supply inlets 10, and a through hole 3d defining a common ink chamber 1 formed therein; and 4, a vibration plate that is resiliently deformed while abutted against the tips of piezoelectric vibration elements 6. A substrate unit 5 is formed by fixing the nozzle plate 2 and the vibration plate 4 to both surfaces of the flow path forming plate 3 so as to be watertight. Reference numeral 7 denotes a base into which the piezoelectric vibration elements 6 are inserted so that the piezoelectric vibration elements can vibrate therein. The ink jet recording head is fabricated into a single body by fixing the piezoelectric vibration elements 6 and the substrate unit 5 with the vibration plate 4 abutted against the tips of the piezoelectric vibration elements 6 exposed from openings of the base. It should be noted that reference numeral 12 in Fig. 1 denotes an ink supply pipe for supplying ink from a not shown ink tank to the substrate unit 5. Fig. 2 shows an embodiment of the piezoelectric vibration element 6. A plurality of layers, each being formed by interposing a piezoelectric material layer 60 between electrode layers 61, 62, are laminated one upon another to form a laminated member. Ends of the electrode layers 61 and ends of the electrode layers 62 are exposed to ends of the laminated member so as to be connected to a segment electrode 62 and a common electrode 64, respectively, so that the piezoelectric vibration element 6 can expand and contract in directions parallel with the electrode layers 61, 62. Fig. 3 is a diagram showing how the substrate unit 5 and the piezoelectric vibration elements 6 are mounted. The nozzle plate 2 and the vibration plate 4 interpose the flow path forming plate 3 therebetween and are fixed to both surfaces of the flow path forming plate 3 with an adhesive so as to be watertight, so that the pressure producing chambers 9 are formed so as to extend along the arrays of the nozzle openings 1. On the other hand, in the vibration plate 4 an island portion 4a is formed so as to be positioned in an almost middle of a region confronting the corresponding pressure producing chamber 9, and a first thick wall portion 4b, and second and third thick wall portions 4c, 4d are also formed. The island portion is abutted against the tip of the piezoelectric vibration element 6. The first thick wall portion 4b is formed so as to confront a partition wall 3c partitioning the adjacent pressure producing chambers 9 and either coincide with the boundary of the pressure producing chamber 9 or slightly overhang the pressure producing chamber 9 as shown in Fig. 3. The third and fourth thick wall portions 4c, 4d are formed so as to slightly overhang both ends of the pressure producing chamber 9. A region, which is a thin wall portion surrounded by the first, second, and third thick wall portions 4b, 4c, 4d, is defined as a diaphragm portion 4e. The diaphragm portion 4e is deformed by the piezoelectric vibration element 6. If the diaphragm portion 4e is formed to a size smaller than the opening of the pressure producing chamber 9 so that the thick wall portions 4b, 4c, 4d of the vibration plate 4 overhang the pressure producing chamber 9, the first thick wall portion 4b overhangs the pressure producing chamber 9 by ΔL1 from the wall 3c defining the pressure producing chambers (Fig. 5), and the second and third thick wall portions 4c, 4e also overhang the pressure producing chamber by ΔL2 in the vicinities of both ends of the pressure producing chamber (Fig. 6). Let us take a specific example, in which the width W1 of the pressure producing chamber 9 is set to 200 µm; the width W2 of the partition wall 3c is set to 80 µm; and the width W3 of the first thick wall portion 4b is set to 140 µm. Then, an overhanging length ΔL1 of 30 µm can be provided in the case where the flow path forming plate 3 and the vibration plate 4 are bonded to each other with the center line of the pressure producing chamber 9 aligned with that of the island portion 4a. As a result, when the diaphragm portion 4e is positioned so as to confront the pressure producing chamber 9 with a positioning error ΔL3 between the flow path forming plate 3 and the vibration plate 4 being equal to, e.g., 20 µm as shown in Fig. 7, an adhesive P overflow region ΔL4 of as large as 10 µm can be provided. As a result, even if the adhesive P overflows from the partition wall 3c, such overflown adhesive P is absorbed by the first, second, and third thick wall portions 4b, 4c, 4d to thereby block the adhesive P from further overflowing to the diaphragm portion 4e, which in turn allows the diaphragm portion 4e to maintain a consistent resilient characteristic. That is, if the vibration plate 4 and the flow path forming plate 3 are misaligned with the thick wall portion 4b formed so as to coincide with the width of the partition wall 3c of the pressure producing chamber 9, the adhesive P overflows into the diaphragm portion 4e, making the vibration characteristic of the diaphragm portion 4e erratic. In general, when the width W3 of the first thick wall portion 4b confronting the partition wall 3c is increased by about 5 to 50% with respect to the width W2 of the partition wall 3c defining the adjacent pressure producing chambers 9, fabrication errors can be absorbed, and the ink jetting performance can therefore be maintained consistent. On the other hand, the diaphragm portion 4e is defined by the frame-like second and third thick wall portions 4c, 4d whose thickness is substantially the same as that of the island portion 4a as well as by the first thick wall portion 4b being integrally formed with the second and third thick wall portions and extending in parallel with the partition wall 3c of the pressure producing chamber 9. As a result, the partition wall 3c defining the pressure producing chamber 9 is reinforced not only by the nozzle plate 2 but also by the first thick wall portion 4b of the vibration plate 4, which in turn increases the rigidity of the substrate unit 5 as a whole with respect to the displacement of the piezoelectric vibration element 6. Hence, the flexion of the substrate unit 5 at the time the ink is jetted can be minimized, thereby preventing crosstalks. Further, as shown in Fig. 8, the second and third thick wall portions 4c, 4d formed on both ends of the pressure producing chamber 9 extend toward the piezoelectric vibration element 6 so as to go along with the partition wall 3c of the pressure producing chamber 9, and the extended regions (the regions shown by dots in Fig. 3) are supported by the base 7 while fixed to the base 7 with the adhesive. Therefore, a nonsupported region S2 becomes shorter than the nonsupported region S1 (Fig. 14) in the conventional example, making flexion of the substrate unit 5 due to displacement of the piezoelectric vibration element 6 smaller. The vibration plate 4 may be formed by electroforming nickel, chromium, or the like for forming the island portion 4a and the thick wall portions 4b, 4c, 4d on a high molecular film such as polyimide, polysulfone, polycarbonate, polyetherimide, polyethylene, polyalamide, or polyester; or by laminating the high molecular film on a metal film such as nickel, chromium, stainless steel, gold, silver, copper, or titanium by casting or the like and etching the metal film so as to match the profiles of the island portion 4a and the thick wall portions 4b, 4c, 4d; or by using a metal film such as silicon, nickel, chromium, stainless steel, or titanium and partially etching a region for forming the diaphragm portion 4e. A 40 µm-thick stainless steel film and a 3 µm-thick polyimide film were laminated by bonding, and the stainless steel film was etched to prepare the vibration plate 4 in this embodiment. Fig. 9 shows a second embodiment of the invention. The second embodiment is characterized as causing only portions close to both ends of the pressure producing chamber 9 (regions A, B in Fig. 9) out of the first thick wall portion formed on the vibration plate 4 to overhang the pressure producing chamber, and causing the width of a region (a region C in Fig. 9) of the first thick wall portion confronting the island portion 4a to coincide with the width of the partition wall 3c defining the pressure producing chamber 9. According to the second embodiment, the area of the diaphragm portion 4e can be increased only if accuracy in aligning the vibration plate 4 with the flow path forming plate 3 is improved. In addition, the region fixed by the base 7 can be made as large as possible, i.e., the nonsupported region 52 can be shortened to reduce flexion of the substrate unit 5. Fig. 10 shows a third embodiment of the invention. The third embodiment is characterized as making the second and third thick wall portions 4c, 4d formed close to both ends of the pressure producing chamber 9 peninsula-like by extending these thick wall portions 4c, 4d to such a degree as to reach both ends of the island portion 4a (regions A, B in Fig. 10), and replacing the first thick wall portion 4b with a thin wall portion 4f. According to the third embodiment, the region supported by the base 7 is made as long as possible to reduce flexion of the substrate unit 5. If the adhesive for bonding the substrate unit 5 to the base 7 is applied by transferring, the region to which the adhesive is applied can be limited within the peninsula-like thick wall portions, thereby preventing the adhesive for fixing the base 7 from overflowing as far as to the diaphragm portion 4e. In this embodiment, a bonding process between the base 7 and the thick wall portions 4c and 4d is performed at a region defined between an inner side of the pressure producing chamber 9 and outer sides of both ends of the island portion 4a in order to prevent the base 7 and the island portion 4a from being contacted from each other by a vibration of the vibration plate 4 when the ink expelling operation is performed. Fig. 11 shows a fourth embodiment of the invention. The fourth embodiment is characterized as forming the first thick wall portion 4b in a region (a region C in Fig. 11) confronting the island portion so as to be continuous to the aforementioned peninsula-like second and third thick wall portions 4c, 4d so that the width of the first thick wall portion 4b is slightly smaller than the partition wall 3c. According to the fourth embodiment, not only the rigidity of the substrate unit as a whole can be improved and the area of the diaphragm portion 4e can be made as large as possible, but also the region supported by the base 7 can be increased to prevent flexion of the substrate unit 5. While the example in which the piezoelectric vibration element of vertical vibration mode is used as a drive source has been described in the aforementioned embodiments, a piezoelectric vibration element of flexion vibration mode may also be used. That is, as shown in Fig. 12, a piezoelectric vibration element 20 of flexion vibration mode is bonded onto the surface of the diaphragm portion 4e defined by the thick wall portions 4b, 4c, 4d so as not to come in contact with the thick wall portions 4b, 4c, 4d without forming the island portion 4a. As a result of this construction, the diaphragm portion 4e is contracted to thereby contract a pressure producing chamber 23 formed of a flow path forming plate 21, a second cover plate 24, and the vibration plate 4, which in turn causes ink to be jetted out of a nozzle opening 21 communicating with the pressure producing chamber 23. In this embodiment also, the propagation of vibrations to the adjacent pressure producing chambers 23 can be prevented by the thick wall portions 4b, 4c, 4d. It should be noted that reference numeral 25 denotes an ink supply inlet. As described in the foregoing, the ink jet recording head of the invention is formed by fixing a substrate unit to a base, the substrate unit being formed by laminating and fixing a flow path forming plate, a nozzle plate, and a vibration plate with an adhesive so as to be watertight, the flow path forming plate having through holes defining pressure producing chambers, ink supply inlets, and a common ink chamber, the nozzle plate having nozzle openings communicating with the pressure producing chambers, the vibration plate having diaphragm portions, each diaphragm portion being resiliently deformed in response to displacement of a piezoelectric vibration element, and in such ink jet recording head, the vibration plate has frame-like thick wall portions formed close to a side of the ink supply inlet of the pressure producing chamber and to a side of the nozzle opening, the thick wall portions being thicker than the diaphragm portion and extended so as to be island-like toward the piezoelectric vibration element, and a region confronting the frame-like thick wall portions is made to serve as a region for bonding the substrate unit to the base. As a result of this construction, the nonsupported region of the pressure producing chamber can be shortened without disturbing the displacement of the diaphragm portion, which in turn reduces flexion of the substrate unit attributable to displacement of the piezoelectric vibration element.

Claims: A substrate unit (5) for an ink jet recording head, comprising: a flow path forming plate (3) having pressure producing chambers (9); a nozzle plate (2) having nozzle openings (1) communicating with said pressure producing chambers (9); and a vibration plate (4), wherein said vibration plate (4) comprises at least a diaphragm portion (4e) being deformable, and at least a thick wall portion (4b,4c,4d) being thicker than the diaphragm portion (4e), so that the diaphragm portion (4e) confronts an opening in the pressure producing chambers (9), said diaphragm portion (4e) being formed to a size smaller than the opening of the pressure producing chambers (9), so that the thick wall portion (4b,4c,4d) overhangs portions of the pressure producing chambers (9). The substrate unit (5) according to claim 1, wherein at the region confronting said partition wall (3c) the thick wall portion (4b,4c,4d) is peninsula like. The substrate unit (5) according to claim 1 or 2, wherein the substrate unit (5) is formed by laminating and fixing the flow path forming plate (3), the nozzle plate (2) and the vibration plate (4). The substrate unit (5) according to any of the preceding claims, wherein the flow path forming plate (3) further comprises ink supply inlets (10) and a common ink chamber. The substrate unit (5) according to any of the preceding claims, wherein the diaphragm portion (4e) is resiliently deformable in response to displacements of a piezoelectric element (6), and the thick wall portion (4b,4c,4d) is formed frame-like close to at least both of the pressure producing chambers (9) and/or extended so as to be island-like toward the piezoelectric vibration element (6). The substrate unit (5) according to claim 5, wherein a region confronting the frame-like thick wall portion is made to serve as a region for bonding the substrate unit (5) to a base (7). The substrate unit (5) according to claim 6, wherein a region of the frame-like thick wall portion (4b,4c,4d) is closer to the piezoelectric vibration element (6) than at least both ends of the pressure producing chamber (9) and is made to serve as a region for bonding the substrate unit (5) to the base (7). The substrate unit (5) according to claim 6, wherein the base (7) is bonded to the substrate unit (5) with a predetermined pitch defined between the base (7) and the diaphragm portion (4e). The substrate unit (5) according to any of the preceding claims, wherein an island portion (4a) is formed at a region confronting the pressure producing chamber (9), and the island portion (4a) corresponds to a thick wall portion (4b,4c,4d). The substrate unit (5) according to one of the preceding claims, wherein the thick wall portion (4b,4c,4d) is extended so as to confront a partition wall (3c) defining the pressure producing chamber (9). The substrate unit (5) according to any of the preceding claims, wherein the thick wall portion (4b,4c,4d) is discontinuous at a region confronting a piezoelectric vibration element (6). The substrate unit (5) according to claim 1 or 2, wherein the thick wall portion (4b,4c,4d) is formed close to a side of the ink supply inlet (10) of the pressure producing chamber (9) and to a side of the nozzle opening (1). The substrate unit (5) according to any of the preceding claims, wherein a width (W 3 ) of the thick wall portion (4b,4c,4d) at a region confronting a partition wall (3c) defining the pressure producing chamber (9), is set to a value 5 to 50% larger than a width (W 2 ) of a partition wall (3c) defining the pressure producing chamber (9). An ink jet recording head comprising a substrate unit (5) according to any of the preceding claims.

Inventors: MIURA KAZUHIKO, NAKA TAKAHIRO, OKAZAWA NORIAKI, SUZUKI KAZUNAGA, USUI MINORU, MIURA, KAZUHIKO, NAKA, TAKAHIRO, OKAZAWA, NORIAKI, SUZUKI, KAZUNAGA, USUI, MINORU, MIURA, KAZUHIKO, C/O SEIKO EPSON CORPORATION, NAKA, TAKAHIRO, C/O SEIKO EPSON CORPORATION, OKAZAWA, NORIAKI, C/O SEIKO EPSON CORPORATION, SUZUKI, KAZUNAGA, C/O SEIKO EPSON CORPORATION, USUI, MINORU, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1994
Main classification: B41J2
IPC codes: B41J2